The Herald - The World of Geoe, #1

The future of Earth depends on unwanted misfits. Argrenn and his wife were saved from Earth's destruction by the Vrelth and transported to Geoe, a world run with gaming rules. They need to get a message out to other human planets but the Vrelth turned Geoe into a war zone. The only protection they have is their new friends and the rules of the game - none of which they know. Either they learn to play the game or Earth is doomed.